@gollum,
Hulu.com isn't like that when it comes to movies and television shows.
They show complete television episodes and movies where they have gotten the rights by the producers and studios of the said products. When they don't have the rights to air the complete film or television episode then they get the right to air clips.
For example: Saturday Night Live is one where they show most of the episodes but have to cut it up because of their agreement with NBC. I believe they never air the musical guest because its the deal NBC has with the music recording company and they probably see that being able to see the concert guest on demand might cut into their record sales. In truth, the opposite is most likely true. The more exposure the people see of these bands the likelier they sell more singles and albums.
And as it already had been said, Youtube has a file size limit that restricts those who upload the videos onto the Youtube servers. An inconvenience to the viewer as it may especially since it was their policy to restrict bandwidth when the site first started and bandwidth was limited for the site but no longer is an issue now.